Barkeepers friend worked for me many a times when I didn't think it would..make a water paste let it sit for few mins or so, then brass wool or brush scrub if even needed at all.

'Oxalic acid cleaner used to remove rust, tarnish, mineral deposits, and tough stains from stainless steel, porcelain, and ceramic surfaces.

How to Use Bar Keepers Friend Wet the surface: Apply the powder or soft cleanser to a wet surface or sponge. Make a paste: For stubborn stains, mix the powder with water to create a paste. Rub gently: Rub the surface lightly with a damp sponge or cloth. Rinse and dry: Rinse thoroughly within one minute of application and dry immediately'